Url Form Action Without ViewContext - asp.net-mvc

Question

Is it possible to get a URL from an action without knowing ViewContext (e.g., in a controller)? Something like this:
LinkBuilder.BuildUrlFromExpression(ViewContext context, Expression<Action<T>> action)
...but using Controller.RouteData instead of ViewContext. I seem to have metal block on this.

Answer 1

Here's how I do it in a unit test:
private string RouteValueDictionaryToUrl(RouteValueDictionary rvd)
{
var context = MvcMockHelpers.FakeHttpContext("~/");
// _routes is a RouteCollection
var vpd = _routes.GetVirtualPath(
new RequestContext(context, _
routes.GetRouteData(context)), rvd);
return vpd.VirtualPath;
}
Per comments, I'll adapt to a controller:
string path = RouteTable.Routes.GetVirtualPath(
new RequestContext(HttpContext,
RouteTable.Routes.GetRouteData(HttpContext)),
new RouteValueDictionary(
new { controller = "Foo",
action = "Bar" })).VirtualPath;
Replace "Foo" and "Bar" with real names. This is off the top of my head, so I can't guarantee that it's the most efficient solution possible, but it should get you on the right track.

Answer 2

Craig, Thanks for the correct answer. It works great, and it also go me thinking. So in my drive to eliminate those refactor-resistent "magic strings" I have developed a variation on your solution:
public static string GetUrlFor<T>(this HttpContextBase c, Expression<Func<T, object>> action)
where T : Controller
{
return RouteTable.Routes.GetVirtualPath(
new RequestContext(c, RouteTable.Routes.GetRouteData(c)),
GetRouteValuesFor(action)).VirtualPath;
}
public static RouteValueDictionary GetRouteValuesFor<T>(Expression<Func<T, object>> action)
where T : Controller
{
var methodCallExpresion = ((MethodCallExpression) action.Body);
var controllerTypeName = methodCallExpresion.Object.Type.Name;
var routeValues = new RouteValueDictionary(new
{
controller = controllerTypeName.Remove(controllerTypeName.LastIndexOf("Controller")),
action = methodCallExpresion.Method.Name
});
var methodParameters = methodCallExpresion.Method.GetParameters();
for (var i = 0; i < methodParameters.Length; i++)
{
var value = Expression.Lambda(methodCallExpresion.Arguments[i]).Compile().DynamicInvoke();
var name = methodParameters[i].Name;
routeValues.Add(name, value);
}
return routeValues;
}
I know what some will say...dreaded reflection! In my particular application, I think the benefit of maintainability outweighs performance conerns. I welcome any feedback on this idea and the code.